We didn’t actually buff Tome of Light per se. It was just twice as good as the tooltip said it was, and since we didn't think that a nerf was in order, we're just correcting the tooltip for 4.3. You guys shouldn't notice a change to Tome of Light.

You should notice a change to Holy Word: Serenity, though. As you know, that ability hasn't always benefited from the 25% crit bonus that it's supposed to get. It was a little tricky to figure out why that was happening, but we've gotten to the bottom of it. Holy Word: Serenity should be fixed for 4.3, so you should notice a change there.

I just tested and this is not accurate on live. Did this post mean that on the PTR you accidentally buffed Tome of Light, and then decided to just run with it and update the tooltip instead of revert the buff?

Yes, that's correct. Sorry for the confusion! The bug came in an earlier version of 4.3 and was fixed recently in 4.3. Please recall that, while you guys are just getting your first look at it, internally we have been working on 4.3 for a long time.

However, this fix has introduced another bug. With the priest tier set bonus, the duration of Sanctuary can be longer than its cooldown. This causes a host of technical problems because that spell just isn’t set up right to have multiple copies, nor do we really want Sanctuary to have 100% uptime in the first place. So, we're likely to revert the change to Tome of Light (restoring it back to 15% / 30%) but we'll also lower the base cooldown of Serenity so that it will have a 7 sec cooldown with Tome of Light.

Note: All of this discussion applies to the 4.3 PTR, where some amount of "design churn" is to be expected; we want to avoid making you to feel like your character is under a barrage of constant changes after a patch goes live.